Locusts

Voracious insects related to grasshoppers and crickets (and therefore presumably also to the 'neekerbreekers' of Midgewater Marshes). Locusts are famed for forming immense and destructive swarms, and indeed our only reference to them comes from a simile describing the bats massing over Bolg's army as being like such a swarm. These words (spoken by Gandalf) imply that locusts were known in Middle-earth, but they are never encountered or described directly.